add runtime script and mount

packages/svelte/src/devtool/index.js

@@ -1,2 +1,3 @@
 export {default as DevTool} from './DevTool.svelte'
 export * from './configure.js'
+export {mountUI as default} from './runtime.js'

packages/svelte/src/devtool/runtime.js

@@ -0,0 +1,21 @@
+import DevTool from './DevTool.svelte';
+import { mount } from 'svelte';
+function create_devtool_host() {
+	const id = 'svelte-devtool-host';
+	if (document.getElementById(id) != null) {
+		console.debug('svelte-devtool-host already exists, skipping');
+		return;
+	}
+	const el = document.createElement('div');
+	el.setAttribute('id', id);
+	// appending to documentElement adds it outside of body
+	document.documentElement.appendChild(el);
+	return el;
+}
+export function mountUI(){
+	if(typeof window !== 'undefined') {
+		mount(DevTool, { target: create_devtool_host() });
+	}
+}
+
+